Optical systems and methods and optical amplifiers for use therein

ABSTRACT

Optical transmission systems of the present invention include at least one optical amplifier in which pump power being provided to an amplifying medium is amplified using a pump amplifier prior to being introduced into the amplifying medium. In various embodiments, a cascaded Raman resonator is used as a pump booster source to provide Raman amplification of the pump power being supplied from one or more pump sources to the signal channel amplifying medium.

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] Not Applicable

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

[0002] Not Applicable

BACKGROUND OF THE INVENTION

[0003] The present invention is directed generally to opticaltransmission systems. More particularly, the invention is directedtoward optical transmission systems including higher performance opticalamplifiers.

[0004] Digital technology has provided electronic access to vast amountsof information. The increased access has driven demand for faster andhigher capacity electronic information processing equipment (computers)and transmission networks and systems to link the processing equipment.

[0005] In response to this demand, communications service providers haveturned to optical communication systems, which have the capability toprovide substantially larger information transmission capacities thantraditional electrical communication systems. Information can betransported through optical systems in audio, video, data, or othersignal format analogous to electrical systems. Likewise, optical systemscan be used in telephone, cable television, LAN, WAN, and MAN systems,as well as other communication systems.

[0006] Early optical transmission systems, known as space divisionmultiplex (SDM) systems, transmitted one information signal using asingle wavelength in separate waveguides, i.e. fiber optic strand. Thetransmission capacity of optical systems was increased by time divisionmultiplexing (TDM) multiple low bit rate, information signals into ahigher bit rate signals that can be transported on a single opticalwavelength. The low bit rate information carried by the TDM opticalsignal can then be separated from the higher bit rate signal followingtransmission through the optical system.

[0007] The continued growth in traditional communications systems andthe emergence of the Internet as a means for accessing data has furtheraccelerated the demand for higher capacity communications networks.Telecommunications service providers, in particular, have looked towavelength division multiplexing (WDM) to further increase the capacityof their existing systems.

[0008] In WDM transmission systems, pluralities of distinct TDM or SDMinformation signals are carried using electromagnetic waves havingdifferent wavelengths in the optical spectrum, typically in the infraredportion of the spectrum. The pluralities of information carryingwavelengths are combined into a multiple wavelength WDM optical signalthat is transmitted in a single waveguide. In this manner, WDM systemscan increase the transmission capacity of existing SDM/TDM systems by afactor equal to the number of wavelengths used in the WDM system.

[0009] Optical WDM systems were not initially deployed, in part, becauseof the high cost of electrical signal regeneration equipment requiredapproximately every 20-50 km to compensate for signal attenuation foreach optical wavelength throughout the system. The development of theerbium doped fiber optical amplifier (EDFA) provided a cost effectivemeans to optically amplify attenuated optical signal wavelengths in the1550 nm range. In addition, the 1550 nm signal wavelength rangecoincides with a low loss transmission window in silica based opticalfibers, which allowed EDFAs to be spaced further apart than conventionalelectrical regenerators.

[0010] The use of EDFAs essentially eliminated the need for, and theassociated costs of, electrical signal regeneration/amplificationequipment to compensate for signal attenuation in many systems. Thedramatic reduction in the number of electrical regenerators in thesystems, made the installation of WDM systems in the remainingelectrical regenerators a cost effective means to increase opticalnetwork capacity.

[0011] WDM systems have quickly expanded to fill the limited amplifierbandwidth of EDFAs. New erbium-based fiber amplifiers (L-band) have beendeveloped to expand the bandwidth of erbium-based optical amplifiers.Also, new transmission fiber designs are being developed to provide forlower loss transmission in the 1380-1530 nm and 1600-1700 nm ranges toprovide additional capacity for future systems.

[0012] Raman fiber amplifiers (“RFAs”) are also being investigated foruse in wide bandwidth, e.g., 100 nm, optical amplifiers, but RFAsgenerally make less efficient use of pump power than EDFAs. Therefore,RFAs have not been deployed in commercial systems because significantpump powers on the order of hundreds of milliwatts are required toachieve the required levels of amplification.

[0013] RFAs do, however, have appeal as a viable option for nextgeneration optical amplifiers, because RFAs provide low noise, widebandwidths, and wavelength flexible gain.

[0014] Commonly assigned U.S. patent application Ser. Nos. 09/119,556and 09/253,819, which are incorporated herein by reference, describeRFAs that can be deployed in existing fiber optic networks havingvarious fiber designs and compositions and over a wide range of signalwavelengths.

[0015] RFAs are theoretically scalable to provide amplification over arange of bandwidths and power. However, the amplification bandwidth andpower is limited, in part, by the amount of pump power that can bedelivered to the fiber amplifier. The capability to provide higher pumppowers is essential for continued development of optical amplifiers andoptical systems to meet the requirements of next generation opticalsystems.

BRIEF SUMMARY OF THE INVENTION

[0016] The systems, apparatuses, and methods of the present inventionaddress the above needs to provide higher performance optical amplifiersand systems. The optical systems generally include at least one opticaltransmitter configured to transmit information via at least one opticalsignal wavelength, or channel, to at least one optical receiver viaoptical transmission media, such as an optical fiber. The system willalso include at least one optical amplifier disposed between thetransmitters and receivers to overcome various signal power losses, suchas media attenuation, combining, splitting, etc. in the system.

[0017] The optical amplifier will generally include an optical signalamplifying medium supplied with pump power in the form of optical energyin one or more pump wavelengths via an optical pump source. The pumpsource can include one or more optical sources, such as narrow and broadband lasers or other coherent, as well as incoherent sources.

[0018] The optical amplifier will further include a pump amplifierconfigured to amplify the pump power being supplied to the signalamplifying media. In various embodiments, the pump amplifier includes apump amplifying medium supplied with pump booster power in the form ofoptical energy from a pump booster source. The pump amplifying mediumcan include various amplifying fibers as may be appropriate foramplifying the pump power. The pump amplifier can be configured toprovide Raman amplification of the pump power being supplied to at leastone amplifying media to optically amplify signal wavelengths passingthrough the amplifying media. For example, the pump booster power can besupplied in the 1300-1450 range to provide Raman amplification of pumpwavelengths in the 1400-1500 range in the pump amplifier.

[0019] In addition, the pump booster power can be split and used toamplify pump power being supplied to multiple optical amplifiersdisposed along one or more transmission fibers. In this manner, the pumpbooster power, which can be several watts, and the cost of the pumpbooster source can be spread over a number of amplifiers in the system.It may be also be desirable to combine the power from two or more pumpbooster source prior to splitting the pump booster power to amplify theRFA pump wavelengths to provide additional redundancy in the system.

[0020] In various embodiments, a cascaded Raman resonator (“CRR”) and/orsemiconductor laser diodes can be used as the pump booster source toprovide pump booster power to amplify the pump power provided by thepump sources. The pump power supplied by each of the optical sources inthe pump source can be varied to control the overall pump powerdistribution over the pump wavelength range.

[0021] In various CRR embodiments, CRR input power in at least one inputwavelength is introduced into a fiber Raman resonator ring via an inputwavelength division multiplexing (WDM) coupler. An output WDM coupler isfurther coupled to resonator ring to output the pump booster power at anappropriate wavelength to supply optical energy for use in the pumpamplifying fiber.

[0022] The use of pump amplifier external to the transmission fiber inthe present invention provides flexibility in the optical amplifierdesign. For example, lower power optical sources can be employed in thepump sources, thereby reducing component costs in the system. Theoptical sources can be individually controlled and fine tuned before thepump power is amplified. When Raman pump amplifiers are used, thewavelength and relative power of the optical sources can be variedwithin the Raman gain bandwidth of the pump amplifier to vary thewavelength profile of the pump power provided to the amplifier withoutchanging the pump amplifier. Thus, the optical amplifiers of the presentinvention provide increased power, control, flexibility, andupgradability necessary for higher performance optical systems. Theseadvantages and others will become apparent from the following detaileddescription.

BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Embodiments of the present invention will now be described, byway of example only, with reference to the accompanying drawings for thepurpose of illustrating present embodiments only and not for purposes oflimiting the same, wherein like members bear like reference numeralsand:

[0024]FIGS. 1 and 2 show optical system embodiments;

[0025] FIGS. 3-4 show optical amplifier embodiments; and,

[0026] FIGS. 5-8 show various optical amplifier and pump amplifierembodiments.

DETAILED DESCRIPTION OF THE INVENTION

[0027] Optical systems 10 of the present invention include an opticalamplifier 12 disposed along an optical transmission medium, such as anoptical fiber 14, to optically amplify optical signals passing betweenoptical processing nodes 16. One or more transmitters 18 can be includedin the nodes 16 and configured to transmit information via the opticalsignals in one or more information carrying signal wavelengths, orsignal channels, λ_(si) to one or more optical receivers 20 in othernodes 16. The optical system 10 can be controlled by a networkmanagement system 22 and configured in multi-dimensional networks(FIG. 1) or in one or more serially connected point to point links (FIG.2). The network management system 22 can communicate with the variousnodes and elements in the optical systems 10 via wide area networksexternal to the system 10 and/or supervisory optical channels within thesystem 10.

[0028] The optical processing nodes 16 may also include other opticalcomponents, such as one or more add/drop devices and optical andelectrical switches/routers/cross-connects 21 interconnecting thetransmitters 18 and receivers 20. For example, broadcast and/orwavelength reusable, add/drop devices, and optical andelectrical/digital cross connect switches and routers can be configuredvia the network management system 22 in various topologies, i.e., rings,mesh, etc. to provide a desired network connectivity.

[0029] The transmitters 18 used in the system 10 will generally includea narrow bandwidth laser optical source that provides an opticalcarrier. The transmitters 18 also can include other coherent narrow orbroad band sources, such as sliced spectrum sources, as well as suitableincoherent optical sources as appropriate. Information can be impartedto the optical carrier either by directly modulating the optical sourceor by externally modulating the optical carrier emitted by the source.Alternatively, the information can be imparted to an electrical carrierthat can be upconverted using the optical carrier onto an opticalwavelength to produce the optical signal. Similarly, the opticalreceiver 20 used in the present invention can include various detectiontechniques, such coherent detection, optical filtering and directdetection, and combinations thereof. Employing tunable transmitters 18and receivers 20 in the optical nodes 16 in a network, such as in FIG.2, can provide additional versatility in the system 10.

[0030] The transmitters 18 and receivers 20 can be also connected tointerfacial devices 23, such as electrical and optical cross-connectswitches, IP routers, etc., to provide interface flexibility within, andat the periphery of, the optical system 10. The interfacial devices 23can be configured to receive, convert, and provide information in one ormore various protocols, encoding schemes, and bit rates to thetransmitters 22, and perform the converse function for the receivers 24.The interfacial devices 23 also can be used to provide protectionswitching in various nodes 16 depending upon the configuration.

[0031] Generally speaking, N transmitters 18 can be used to transmit Mdifferent signal wavelengths to J different receivers 20. In variousembodiments, one or more of the transmitters 18 and/or receivers 20 canbe wavelength tunable to provide wavelength allocation flexibility inthe optical system 10. In addition, the system 10 can also be configuredto carry uni- and bi-directional traffic.

[0032] Optical combiners 24 can be used to combine the multiple signalchannels into WDM optical signals and pump wavelengths λ_(pi). Likewise,optical distributors 26 can be provided to distribute the optical signalto the receivers 20 _(j) and optical signal and pump wavelengths λ_(pi)to multiple paths. The optical combiners 24 and distributors 26 caninclude various multi-port devices, such as wavelength selective andnon-selective (“passive”), fiber and free space devices, as well aspolarization sensitive devices. The multi-port devices can variousdevices, such as circulators, passive, WDM, and polarizationcouplers/splitters, dichroic devices, prisms, diffraction gratings,arrayed waveguides, etc. The multi-port devices can be used alone or invarious combinations along with various tunable or fixed wavelengthfilters in the optical combiners 24 and distributors 26. The filters caninclude various transmissive or reflective, narrow or broad bandfilters, such as Bragg gratings, Mach-Zehnder, Fabry-Perot and dichroicfilters, etc. Furthermore, the combiners 24 and distributors 26 caninclude one or more stages incorporating various multi-port device andfilter combinations to multiplex, consolidate, demultiplex, multicast,and/or broadcast signal channels λ_(si) and pump wavelengths λ_(pi) inthe optical systems 10.

[0033] The optical amplifiers 12 generally include an optical amplifyingmedium 30 supplied with power from an amplifier power source 32 as shownin FIG. 3. For the sake of clarity, the optical amplifier 12 will begenerally described in terms of an amplifying fiber 34 supplied withpump power in the form of optical energy from one or more pump sources36, examples of which are shown in FIGS. 4a-d. It will be appreciatedthat optical amplifiers 12 could include planar optical amplifyingdevices, and can be used in combination with semiconductor amplifiers.

[0034] The amplifying fiber 34 will generally be a doped and/or Ramanfiber supplied with pump power in one or more pump wavelengths λ_(pi)suitable for amplifying the signal wavelengths λ_(si) passing throughthe amplifying fiber 34. One or more dopants can be used in the dopedamplifying fiber 34, such as Er, other rare earth elements, as well asother dopants. The Raman fibers can include various silica-based fibers,e.g., pure, P-doped and/or Ge-doped silica fibers, such as thosecommonly used as transmission fiber, dispersion compensating fiber,etc., as well as other fiber material suitable for providing Raman gain.The doped and Raman fiber can be supplied in optical energy in variouspump wavelengths to amplify signal channels in other wavelengths. Forexample, signal channels in the 1550 nm wavelength range can beamplified by pumping an erbium doped fiber with pump power at variouswavelengths, such as 1480, and 980 nm. Likewise, Raman fibers can besupplied with pump power over a wavelength range, such as 1450-1480 nmto amplify signal channels in the 1550 nm wavelength range. Other signalwavelengths ranges can also be employed, for example 1300 nm, in theoptical system 10 as may be desired.

[0035] The amplifying fiber 34 can have the same or differenttransmission and amplification characteristics than the transmissionfiber 14. For example, dispersion compensating fiber, dispersion shiftedfibers, standard single mode fiber and other fiber types can beintermixed as or with the transmission fiber 14 depending upon thesystem configuration. Thus, the amplifying fiber 34 can serve multiplepurposes in the optical system, such as performing dispersioncompensation and different levels of amplification, as well as losslesstransmission and variable attenuation, of the signal wavelengths λ_(si).

[0036] The optical amplifier 12 can also include one or more serialand/or parallel amplifier stages, which may include combinations of oneor more, distributed and concentrated amplifier stages. The opticalamplifiers 12 may also include remotely pumped doped fiber or Ramanamplifying fibers 34 _(i) having different amplification andtransmission characteristics, e.g., dispersion, etc., than thetransmission fiber 14. The remotely pumped amplifying fiber 34 _(i) canbe pumped with excess pump power supplied to provide Raman gain in thetransmission fiber 14 or via a separate fiber. In addition, the opticalamplifier can include short lumped doped fiber amplifier stages operatedin deep saturation using pump power being supplied to other stages.

[0037] Other optical signal varying devices, such attenuators, filters,isolators, and equalizers can be deployed before, between, and aftervarious stages of the amplifier 12 to decrease the effective lossassociated with devices. Similarly, signal processing devices, such asadd/drop devices, routers, etc. can be included proximate the variousamplifier stages.

[0038] Pump energy can be supplied to the amplifying fiber 34 incounter-propagating and/or co-propagating directions with respect to thepropagation of the signal wavelengths λ_(si), as shown in FIGS. 4a-d. Itwill be appreciated that in a bi-directional system 10, the pumpwavelength λ_(pi) will be counter-propagating relative to signalwavelengths λ_(si) in one direction as well as co-propagating relativeto signal wavelengths λ_(si) in the other direction.

[0039] Pump power can be supplied separately to each amplifier stage orthe pump power can be shared by splitting the pump power before it isintroduced into the amplifier or by streaming excess pump power from onestage to another. In addition, pump reflectors can be used to increasethe pump power utilization in one or more stages.

[0040] The pump source 36 can include one or more narrow and broad bandlasers, or other coherent source, as well as incoherent sources, eachproviding pump power in wavelength bands centered about one or more pumpwavelengths λ_(pi). The pump wavelengths λ_(pi) can be combined usingcombiners 24, such as fused tapered and dichroic couplers, polarizationcombiners, etc., before being introduced into the transmission fiber 14.

[0041] In the present invention, the optical amplifier 12 furtherincludes a pump amplifier 40 configured to amplify the pump power beingprovided to the amplifying media 34. The pump amplifier 40 can bevariously configured similar to the optical amplifier 12 for the signalwavelength λ_(si). The pump amplifier 40 will generally include pumpamplifying medium 42 supplied with pump booster power in the form ofoptical energy in one or more pump booster wavelengths λ_(pbo) from apump booster source 44. It may also be possible to use semiconductoramplifiers as the pump amplifier 40.

[0042] The pump amplifying medium 42 can be specifically tailoreddepending upon the desired amount of gain from the pump amplifier 40.Various types of amplifying medium can be used as discussed with respectto the amplifying medium 34 for the signal wavelengths λ_(si). Unlike inthe amplifying medium 34, the selection of the pump amplifying medium 42is not limited by potential negative affects on the signal wavelengthcharacteristics, because the signal wavelengths λ_(si) do not passthrough pump amplifying medium 42.

[0043] The pump amplifier 40 can be used to provide Raman amplificationof the pump power. For example, the pump booster source 44 can providebooster pump power in the 850 nm and 1350 nm wavelength ranges toprovide Raman amplification of pump wavelengths in the 980 nm and 1450nm wavelength ranges, respectively. The pump booster power can be co-and/or counter-propagated relative to the pump wavelengths, althoughcounter-propagating the pump booster power relative to the pump powermay reduce interactions.

[0044] In various embodiments, the pump booster source 44 includes oneor more high power semiconductor diodes, cascaded Raman resonators(“CRR”), as well as other high power sources, configured to supply pumpbooster power to optically amplify the pump power being supplied to atleast one amplifying media. For example, commercially available CRRsfrom SDL, Inc. (San Jose, Calif.) have output wavelengths in the1450-1480 nm range. CRRs generally include a resonator configured toshift input wavelengths λ_(pbi) of light through one or more Stokesshifts to provide optical energy at successively longer wavelengthsuntil a selected output wavelengths λ_(pbo) is reached. The number ofStokes shift performed by the CRR depends upon the particularconfiguration of the CRR.

[0045] Various CRRs are suitable for use in the present invention. Forexample, U.S. Pat. Nos. 5,323,404 and 5,623,508 describe CRRs that usespaced pairs of Bragg gratings to produce a resonator cavity. Each pairof Bragg gratings corresponds to one of the Stokes wavelengths betweenthe input wavelength and the desired output wavelength. Pairs of highreflectivity Bragg gratings are provided for each Stokes wavelengthintermediate to the input and the output wavelengths. Low reflectivityBragg gratings are provided at the inlet and outlet of the cavity toallow the input and output wavelengths into and out of the cavity,respectively.

[0046] Other CRR designs employ couplers and fiber rings to produce theStokes shift. For example, in PCT International Publication No. WO97/32378 an optical wavelength converter is provided that employs one ormore fiber rings optically linked via couplers to produce acorresponding number of Stokes shifts in the light wavelength. Anothercoupler embodiment incorporates a coupler connecting a fiber ring to alight source and a high reflectivity mirror is discussed by Chernikov etal., Electronics Letters, Apr. 2, 1998, v. 34, n. 7, Online No.19980421.

[0047] The present invention also includes hybrid grating/combiner CRRembodiments that provide increased flexibility over conventional gratingand coupler CRR designs. The hybrid grating/combiner CRR embodimentsemploy input and output wavelength selective combiners, such as WDMcouplers, 46 _(i) and 46 _(o), generally corresponding to the input andoutput wavelengths, λ_(pbi) and λ_(pbo), respectively. Optical fiber 48or other Raman gain medium is used to interconnect two input wavelengthWDM coupler ports 50 _(i1) and 50 _(i2) with two output wavelength WDMcoupler ports 50 _(o1) and 50 _(o2) to produce a resonator cavity 52, asshown in FIGS. 6a&b. The input and output WDM couplers, 46 _(i) and 46_(o), can be designed to have a broad range of bandwidths in the inputand output wavelength range, respectively, to provide flexibility in theselection of the CRR source wavelengths.

[0048] In these embodiments, one or more input wavelengths λ_(pbi) areprovided by an input wavelength source 47, such as one or more lasers,and are selectively introduced into the resonator cavity 52 through athird input coupler port 50 _(i3). The input wavelength travels throughthe resonator cavity 52 and exits through a fourth input coupler port 50_(i4). A high reflectivity (˜100%) reflector 54 _(H) is position toreflect input wavelength light exiting the resonator cavity 52 throughthe fourth input coupler port 50 _(i4) back into the resonator cavity52.

[0049] Similarly, the output wavelength λ_(pbo) light selectively exitsthe resonator cavity 52 from third and fourth output wavelength WDMcoupler ports, 50 _(o3) and 50 _(o4). A low reflectivity (˜10%)reflector 54 _(L) is positioned to reflect a portion of the outputwavelength light λ_(pbo) exiting through the third output coupler port50 _(o3) back into the resonator cavity 52 to provide feedback to theresonantor cavity 52. Another high reflectivity (˜100%) reflector 54_(H) is position to reflect input wavelength light exiting through thefourth output coupler port 50 _(o4) back into the resonator cavity 52.

[0050] The resonator cavity 52 will generally be formed using opticalfiber 54 to interconnect the input and output WDM couplers. The opticalfiber 54 can include one or more optical fiber types that have differentRaman gain and Stoke shifting characteristics relative to the input andoutput wavelengths, λ_(pbi) and λ_(pbo), respectively. For example,small core fibers, such as dispersion compensating fibers, moreefficiently promote Raman gain and can be used to form the resonatorcavity 52. The fiber 54 will generally be formed in rings of variouslengths for ease of handling, but can be formed in other shapes as maybe appropriate.

[0051] The high reflectivity reflectors 54 _(H) can generally be highreflectivity, non-wavelength selective mirrors, although wavelengthselective reflectors, such as Bragg gratings, at the input and outputwavelengths can be used. The use of non-wavelength selective, highreflectivity reflectors provides additional flexibility in theconfiguring the CRR, because the reflectors do not constrain theselection of the input and output wavelengths of the CRR.

[0052] The lower reflectivity, wavelength selective reflector 54 _(L)(“feedback reflector”) provides feedback control over the outputwavelength λ_(pbo). The reflective bandwidth of the feedback reflector54 _(L) can be tailored to meet the required bandwidth of the outputwavelength for a system 10. Also, the feedback reflector 54 _(L) can betunable to provide additional flexibility in the output wavelength.Fixed or tunable fiber Bragg gratings, Fabry-Perot filters, and otherreflective devices, can be used as the high and lower reflectivityreflectors, 54 _(H) and 54 _(L). For example, FIG. 6b shows a morespecific embodiment, in which Bragg gratings are used as reflectors 54.

[0053] In various embodiments, pump booster power can be split and usedto amplify pump power being provided to multiple amplifier stagesdisposed along one or more transmission fibers 14. FIG. 7 shows anexemplary embodiment, the pump booster power is divided using adistributor 26, such as a passive splitter, and supplied to the pumpamplifying fibers 42 in four separate pump amplifiers 40. In thismanner, the pump booster power, which can be several watts and the costassociated with of the pump amplifier 40 can be spread over a number ofoptical amplifiers 12. It may be also be desirable to combine two ormore pump booster sources 44 using a combiner 24, such as a passivecoupler, to provide additional redundancy in the system, as furthershown in FIG. 7.

[0054] Exemplary operation of the amplifier 12 of the present inventionwill be described with regard to a Raman fiber amplifier in which thepump power being supplied to the Raman fiber amplifier is amplifiedusing Raman pump amplifier. Signal wavelengths λ_(si) are transmittedfrom the transmitters 18 to the receivers 20 through one or more of theoptical amplifiers 12 in this example.

[0055] The exemplary optical amplifier 12 is configured to receive pumppower ranging from 1400-1500 nm range to amplify signal wavelengthsλ_(si) in the 1500-1600 nm range via Raman amplification. The pumpsource 36 includes a plurality of laser diodes providing a plurality ofpump wavelengths λ_(pi) that can be counter- and/or co-propagatedrelative to the signal wavelengths λ_(si) depending upon the system 10.The pump power is passed through the pump amplifying fiber 42 and pumpbooster power in the 1300-1440 nm range from the pump booster source 44is counter-propagated through the pump amplifying fiber 42 to provideRaman amplification of the pump power.

[0056] Those of ordinary skill in the art will further appreciate thatnumerous modifications and variations that can be made to specificaspects of the present invention without departing from the scope of thepresent invention. It is intended that the foregoing specification andthe following claims cover such modifications and variations.

What is claimed is:
 1. A method of amplifying signal wavelengthscomprising: providing an optical amplifier configured to receive pumppower as optical energy in at least one pump wavelength and amplifysignal wavelengths passing through the optical amplifier; amplifying thepump power prior to introducing the pump power into the opticalamplifier; and, introducing the amplified pump power into the opticalamplifier to amplify signal wavelengths passing through the opticalamplifier.
 2. The method of claim 1, wherein: said amplifying includesamplifying the pump power via Raman amplification prior to introducingthe pump power into the optical amplifier.
 3. The method of claim 1,wherein: said amplifying includes amplifying the pump power via Ramanamplification by counter-propagating pump booster power relative to thepump power prior to introducing the pump power into the opticalamplifier.
 4. The method of claim 1, wherein said amplifying includesamplifying the pump power by Raman amplification using optical energyprovided by at least one of a cascaded Raman resonator and asemiconductor diode laser.
 5. The method of claim 1, wherein saidintroducing includes introducing the amplified pump power to propagaterelative to the signal wavelengths in at least one ofcounter-propagating and co-propagating directions.
 6. The method ofclaim 1, wherein: said providing includes providing an optical amplifierincluding a plurality of amplifier stages, each stage configured toreceive pump power and amplify signal wavelengths passing through theamplifier stage.
 7. The method of claim 1, wherein: said providingincludes providing a distributed Raman amplifier in which pump power isintroduced into at least a section of transmission fiber carrying thesignal wavelengths.
 8. The method of claim 7, wherein said providingincludes locating at least one section of erbium doped fiber remotely toreceive pump power that has passed through the section of thetransmission fiber.
 9. The method of claim 7, wherein said providingincludes locating at least one section of erbium doped fiber to receivepump power before the pump power passes through the section of thetransmission fiber.
 10. The method of claim 1, wherein said providingincludes providing a lumped Raman amplifier and distributed Ramanamplifier in which the amplifying fiber includes at least a section oftransmission fiber.
 11. The method of claim 10, wherein said providingincludes providing a lumped Raman amplifier in which the pump powerpasses through the lumped Raman amplifier into the distributed Ramanamplifier.
 12. A method of transmitting information comprising:transmitting information as an optical signal carried on at least onesignal wavelength through a first optical transmission fiber; providingat least one optical amplifier in the first optical transmission fiberincluding an amplifying fiber configured to receive pump power asoptical energy in at least one pump wavelength and amplify signalwavelengths passing through the optical amplifier and the transmissionfiber; amplifying the pump power prior to introducing the pump powerinto the optical amplifier; introducing the amplified pump power intothe optical amplifier to amplify signal wavelengths passing through theoptical amplifier; and, receiving the information carried by the atleast one signal wavelength from the first transmission fiber.
 13. Themethod of claim 12, wherein: said transmitting includes transmittinginformation in a plurality of signal wavelengths as a WDM signal; saidproviding includes providing an optical amplifier configured to amplifythe WDM signal; and, said receiving includes receiving the informationcarried by the WDM signal.
 14. The method of claim 12, wherein saidproviding includes providing an optical amplifier including a pluralityof amplifier stages, each stage including an amplifying fiber configuredto separately receive pump power as optical energy in at least one pumpwavelength.
 15. The method of claim 12, wherein said providing includesproviding a second optical amplifier in a second transmission fiberconfigured to receive second pump power as optical energy in at leastone pump wavelength and amplify signal wavelengths passing through thesecond optical amplifier and the second transmission fiber; and, saidamplifying includes amplifying the pump power by Raman amplificationusing optical energy provided a common pump booster source prior tointroducing the pump power into the corresponding optical amplifiersprovided in the first and second transmission fibers.
 16. An opticalsystem comprising: at least one transmitter, each configured to transmitinformation via at least one optical signal wavelength; at least onereceiver, each configured to receive at least one of the signalwavelengths; and, at least one optical amplifier supplied with pumppower as optical energy in at least one pump wavelengths disposedbetween said transmitters and receivers and configured to amplify the atleast one signal wavelengths, wherein said optical amplifier includes apump amplifier configured to amplify the pump power before the pumppower is introduced into the optical amplifier.
 17. The system of claim16, wherein said pump amplifier is configured to provide Ramanamplification of the pump power.
 18. The system of claim 16, whereinsaid pump amplifier includes an pump amplifying fiber supplied with pumpbooster power from a pump booster source.
 19. The system of claim 18,wherein said pump booster source is a cascaded Raman amplifer.
 20. Thesystem of claim 19, wherein said cascaded Raman resonator comprises: aninput wavelength combiner having first, second, and third inputwavelength ports; an output wavelength combiner having first, second,and third output wavelength ports; and, a Raman gain medium opticallyconnecting said first and second input wavelength ports with said firstand second output wavelength ports to form a Raman resonator cavity,wherein the pump booster power exits said Raman resonator cavity at theoutput wavelength through said third output wavelength port and opticalenergy is introduced through said third input wavelength port into saidRaman cavity.
 21. The system of claim 20, wherein: said input wavelengthcombiner includes at least a 2×2 WDM coupler having first, second,third, and fourth input wavelength ports; said output wavelengthcombiner includes at least a 2×2 WDM coupler having first, second,third, and fourth output wavelength ports; said fourth input wavelengthport being optical connected to a high reflectivity input reflectorpositioned to reflect input wavelength optical energy exiting said Ramancavity through said fourth input wavelength port back into said Ramancavity; said fourth output wavelength port being optical connected to ahigh reflectivity output reflector positioned to reflect outputwavelength optical energy exiting said Raman cavity through said fourthoutput wavelength port back into said Raman cavity; and, said thirdoutput wavelength port being optical connected to a low reflectivityoutput reflector positioned to reflect a portion of the pump boosterpower in the output wavelength exiting said Raman cavity through saidfourth output wavelength port back into said Raman cavity.
 22. Thesystem of claim 21, wherein said reflectors include fiber Bragggratings.
 23. An optical amplifier comprising: an amplifying mediumconfigured to optically amplify optical signal within said medium usingpump power provided to said amplifying medium; a pump source configuredto provide pump power to said amplifying medium; and, a pump amplifierconfigured to optically amplify the pump power before the pump power isintroduced into the amplifying medium.
 24. The amplifier of claim 23,wherein said amplifying medium includes at least one of a doped fiberand a Raman fiber configured to optically amplify optical signal withinsaid medium using optical pump power provided to said amplifying medium.25. The amplifier of claim 23, wherein said pump amplifier including apump amplifying medium includes at least one of a doped fiber and aRaman fiber configured to optically amplify pump power within said pumpamplifying medium using pump booster power from a pump booster source.